Document Ruby OpenFeature runtime recommendation

[leoromanovsky]

Motivation

Customers need a clear Ruby runtime floor for the full Datadog Feature Flags OpenFeature integration, distinct from general APM tracer support. Without that distinction, teams on older Ruby versions can assume tracing support means provider hooks, exposure logging, and evaluation telemetry are fully covered.

Changes

• Update the Ruby Feature Flags prerequisites to recommend Ruby 3.1 or later for the full OpenFeature integration.
• Clarify that openfeature-sdk 0.5.1 or later is needed for provider hooks, exposure logging, and flag evaluation metrics support.
• Add an info note explaining that older Ruby runtime support remains available for APM tracing, while full Feature Flags telemetry through OpenFeature requires Ruby 3.1 or later.

Decisions

• Document Ruby 3.1 as the minimum recommendation because the OpenFeature Ruby SDK versions with the needed provider hook surface require Ruby >= 3.1.
• Keep this guidance on the Ruby Feature Flags server setup page rather than the generic Ruby tracer support page because the constraint is specific to the Feature Flags/OpenFeature integration.

Related PRs

• Ruby implementation: feat(open_feature): emit server-side EVP flagevaluation dd-trace-rb#5896
• Ruby OpenFeature system-tests surface: Enable Ruby OpenFeature evaluation on older weblogs system-tests#7199
• Ruby OpenFeature runtime documentation: Document Ruby OpenFeature runtime recommendation #37674

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/leo.romanovsky/ruby-openfeature-version-docs/feature_flags/server/ruby